Accelerated heart beat at evening or night time (you usually notice it most then because it is a “quieter” time of day) is, in most of your cases related to OVER-TRAINING.
Be aware of this because it is a sign of your body tending towards a catabolic (muscular breakdown) state - which I’m sure no one here wants.
Also, run a check on the supplements and/or foods you might be eating. I’m assuming you have somewhat clean diets, but it is without question that increasing fruit and vegetable uptake will also “thin” the blood indirectly and also check up on your calcium/phosphorus intake as well as your sodium intake. (Keep calcium and phosphorus in balance)